The present invention relates in general to automotive passive restraint systems, and more particularly to a control circuit for a motorized passive restraint system.
The passive restraint system in a motor vehicle is responsible for providing automatic seatbelt protection to the vehicle occupants. The operation of the system is defined according to certain conditions such as the open or closed position of a door and the occurrence of certain events, such as the turning on of the vehicle ignition switch. As required, a torso belt of the passive restraint system will travel along a track from a forward position to a rearward position to secure an occupant. Other conditions and events will cause the torso belt to travel to the forward position to allow an occupant to enter or leave the vehicle.
The torso belt travels by means of a motor-driven carrier riding in a track along the door frame. As the belt carrier moves from the "A" pillar at the forward position toward the "B" pillar at the rearward position, the torso belt spools out of a retractor usually located at the base of the vehicle seat at the opposite side of the occupant from the door. The unspooling of the torso belt provides sufficient belt length to extend from the retractor, around the vehicle occupant, and to the rearward position of the belt carrier at the "B" pillar.
The belt retractor normally includes a latch mechanism which prevents unspooling of the belt during large accelerations or decelerations, such as in a collision. In the event that the retractor latching mechanism becomes engaged during movement of the belt carrier toward the rearward position, the belt carrier may stall somewhere between the forward and rearward positions since there will be insufficient slack of the torso belt to allow further movement of the belt carrier. This unintended latching of the retractor can occur, for example, when the vehicle occupant adjusts the seat position during belt carrier movement. The sudden movement of the occupant and the seat causes the retractor to latch, and in turn causes the belt carrier to stall.
The belt carrier is driven by a reversible electric motor through a drivebelt which interconnects the belt carrier and the motor. In order to avoid overheating and possible damage to the electric motor during a stall condition, the motor control circuit includes a timer which limits the duration of time for which the motor is energized. A time period is selected which is longer than the normal amount of time required for travel of the belt carrier between opposite positions and is short enough to avoid motor damage in the event of a stalled condition.
When a stall condition occurs due to the latching of the belt retractor, the motor timer can time out thereby removing power from the motor and leaving the belt carrier undesirably stalled somewhere between the forward and rearward positions. Warning lights or audible signals are typically activated to indicate that the belt carrier has not reached the intended position.
In order to deactivate the warning signals in prior art systems, the vehicle occupant must reenergize the passive restraint system to bring the belt carrier into the proper position by either opening a vehicle door or turning the vehicle ignition off and on again.